The present invention relates to a method for lubricating a ceramic-metal interface, such as may be found in an internal combustion engine.
The increased use of ceramic components in passenger cars, such as ceramic valve train components, requires a lubricant which can be used in hybrid ceramic engines. However, high wear losses of metals in contact with ceramics in the presence of conventional lubricants containing zinc dithiophosphate extreme pressure agents are a concern. It has been reported in Lub. Eng., 45, 1989, p. 761, F. Rounds, that interaction among surface-active additives (detergents and dispersants) in lubricants has a negative effect on the anti-wear performance of zinc dithiophosphate at a low load region in the anti-wear regime. The present invention, therefore, provides an improved method for lubricating such ceramic-metal interfaces.
Tribology Transactions, 34 (1991) 417-425 (Preprint No. 90-TC-2C-1, Oct. 8-10, 1990), Gates and Hsu, "Effect of Selected Chemical Compounds on the Lubrication of Silicon Nitride," discloses lubrication of ceramic surfaces with a variety of compounds including organo molybdenum dithiocarbamate and sulfur-molybdenum compounds. Molybdenum-sulfur compounds are reported to only act as friction reducers for silicon nitride unless they also contain phosphorus. When phosphorus is also present, low wear can be obtained in addition to low friction.
Tribology Transactions 32 (1989) 2, 251-257, Yamamoto and Gondo, "Friction and Wear Characteristics of Molybdenum Dithiocarbamate and Molybdenum Dithiophosphate," discloses the use of molybdenum dithiocarbamate in a hydrocarbon baseline oil for reducing friction between surfaces of high carbon chromium bearing steel.
U.S. Pat. No. 4,832,867, Seiki et al., May 23, 1989, discloses a lubricating oil composition which comprises lubricating base oil, at least one organophosphorus compound, and at least one organomolybdenum compound selected from the group consisting of molybdenum oxysulfide alkylphosphorodithioates and molybdenum oxysulfide alkyldithiocarbamates. The lubricating composition is reportedly excellent in antiwear properties, anti-seizure properties, and corrosion resistance, and is suitable for gear oils, bearing oils, internal combustion engine oils, automatic transmission fluids, hydraulic fluid, and metal working fluids.
U.S. Pat. No. 4,846,983, Ward, Jr., Jul. 11, 1989, discloses molybdenum or tungsten thiocarbamate additives for functional fluids, e.g., lubricating oils, automatic transmission fluids, and fuel compositions.